Production of alkali metal polysilicates

ABSTRACT

A METHOD FOR PRODUCING ALKALI METAL POLYSILICATES AND THEIR USE AS BUILDERS IN DETERGENTS IS DISCLOSED. THE POLYSILICATES ARE PRODUCED BY HYDROTHERMALLY REACTING, UNDER CERTAIN CONTROLLED CONDITIONS, AN AQUEOUS DISPERSION OF FINELY-DIVIDED SILICA AND AN ALKALI METAL HYDROXIDE. THE SYTHESIZED REACTION MIXTURE IS THEN SPRAY DRIED AND THE SOLID PRODUCT FRACTURED, PULVERIZED AND AGITATED IN A ROTATING DRUM TO FORM A PRODUCT HAVING PARTICULARLY ADVANTAGEOUS PROPERTIES. THE PRODUCTS OF THE INVENTION CAN BE USED IN ADHESIVES, IN IN THE PRODUCTION OF SILICA GEL, IN TEXTILES AND THE LIKE. HOWEVER, THEIR USE AS BUILDERS IN DETERGENTS AND IN COMBINATION WITH KNOWN ANIONIC, NONIONIC AND AMPHOTERIC SURFACE ACFIVE COMPOUNDS (SURFACTANTS) IS DISCLOSED AND CLAIMED.

Sept 24, i974 O, L BERTORELLI ETAL 3,838,192

PRODUCTION OF LKLI METAL POLYSILICTES Filed Oct. 28, 1971 Sheets-Sheet lSGE 24 1974- 0.1.. BER'TORELLI EY'IV'AL :$838,192

RODUCTION OF ALKALI METAL POLYSILICATES s sheets-sheet s Filed Oct. 28,1971 vUnited States Patent 3,838,192 PRODUCTION OF ALKALI METALPOLYSILICATES Orlando L. Bertorelli and Robert K. Mays, Havre de Grace,and Lloyd E. Williams, Bel Air, Md., and Howard F. Zimmerman, Jr.,Athens, Tenn., assignors to J. M. Huber Corporation, Locust, NJ.

Filed Oct. 28, 1971, Ser. No. 193,485 Int. Cl. C01b 33/32 U.S. Cl.423-334 1 Claim ABSTRACT OF THE DISCLOSURE A method for producing alkalimetal polysilicates and their use as builders in detergents isdisclosed. The polysilicates are produced by hydrothermally reacting,under certain controlled conditions, an aqueous dispersion offinely-divided silica and an alkali metal hydroxide. The synthesizedreaction mixture is then spray dried and the solid product fractured,pulverized and agitated in a rotating drum to form a product havingparticularly advantageous properties. The products of the invention canbe used in adhesives, in the production of silica gel, in textiles andthe like. However, their use as builders in detergents and incombination with known anionic, nonionic and amphoteric surface activecompounds (surfactants) is disclosed and claimed.

BACKGROUND OF THE INVENTION 1. Field of the Invention This inventionrelates to the production of alkali metal silicates and moreparticularly to a unique process for producing alkali metalpolysilicates that may be used as builders in detergents.

2. Description of the Prior Art As known in the art, alkali silicatescan be manufactured by the so-called fusion process wherein a mixture ofsand and an alkali metal salt are fused at temperatures suiciently highto Volatilize the acid radical of the salt used. The glass thus producedis then cooled and dissolved in water, usually at elevated temperaturesand pressures, to yield a product suitable for commercial use. For usein detergents, such silicates are conventionally converted into thehydrated solid for-m by concentrating the solution, removing thesilicates by crystallization and thereafter drying the crystals.

A further known method for producing silicates is the wet digestionmethod wherein a solution of finely divided silica, rendered soluble bydigestion with a concentrated solution of caustic alkali, is evaporatedand cooled to a suitable crystallization temperature.

Examples of the above and further techniques for producing alkali metalsilicates are disclosed in U.S. Pats. 2,161,515; 2,282,018; 2,357,723and 3,271,317.

In this regard, and again as s well known in the art, detergentcompositions conventionally contain a detergent compound i.e., asurfactant and a builder, the latter serving in part, to increase theeiectiveness of the detergent component. While phosphate compounds suchas sodium tripolyphosphate, have been used somewhat extensively asbuilders in detergents for many years, the use of other inorganic saltsincluding alkali metal silicates, carbonates, borates and the like isknown. An example of built detergent compositions disclosing the use ofthe above noted inorganic materials is disclosed in U.S. Pat. 3,392,121which issued July 9, 1968 to Gedge.

ICC

SUMMARY oF THE INVENTION Stated broadly, the present invention isdirected to the production of alkali metal polysilicates which may beused directly in detergents and as replacement for polyphosphates. Theproducts of the invention when used in detergent formulations yieldcompositions with at least equal detergency with formulations containingphosphates and thus are superior to known silicate or other inorganicsalt builders In summary, the unique polysilicates of the presentinvention are produced by the hydrothermal treatment of a dispersion orsuspension of silica and an alkali metal hydroxide. The reactionmixture, upon completion of the hydrothermal synthesis, is spray dried,milled and further processed in a unique manner, as will be described indetail hereinafter, to produce polysilicates having particularlyadvantageous properties. The products of the invention, which may alsobe used in the production of adhesives, silica gel, in textiles, watertreatment and the like, have polysilicate ions in a high polymerized,irreversible state.

It is accordingly a general object of this invention to provide a newand improved process for producing alkali metal polysilicates.

Another and more particular object is to provide an improved product,and a process for preparing same, said product comprising alkali metalpolysilicates having polysilicate ions in a highly polymerized,irreversible state that are functional in the replacement ofpolyphosphates in detergents.

Yet another object is to provide a new and improved process forproducing polysilicates by the hydrothermal reaction of nely dividedsilica and a caustic alkali.

Still another object of the invention is to provide an improved processcomprising the hydrothermal synthesis of alkali metal polysilicates andthe further processing of the synthesized product in a manner such thatthe final product has a relatively high density, low moisture content,and may be used as a direct replacement for phosphates in detergents.Yet still another object is to provide a new and improved process forproducing polysilicates, said process providing high flexibility in theproduction of polysilicates having given or predetermined properties.

The manner in which the foregoing and other objects are achieved inaccordance with the present invention will be better understood in viewof the following detailed description and accompanying drawings, whichform a part of the specification and wherein:

FIG. l is a diagrammatic illustration, shown in elevation, of a suitablearrangement of apparatus for carrying out a particularly advantageousmethod embodiment of the present invention.

FIG. 2 is a diagrammatic illustration shown in elevation of a furtherapparatus embodiment that may be used in the practice of the presentinvention.

FIG. 3 is a pictorial illustration of the product produced in accordancewith the present invention, said product being shown in the various postprocessing steps of the process of the present invention.

FIG. 4 is a photomicrograph of a spray dried product produced in accordwith the present invention.

FIG. 5 is a photomicrograph of a partially fractured and pulversizedproduct of the present invention.

DESCRIPTION OF PREFERRED EMBODIMENT(S) In its broadest aspect, thepresent invention is based on the discovery that alkali metalpolysilicates having particularly desired and predetermined properties,can be produced by hydrothermally reacting or digesting, under certaincontrolled conditions, an aqueous suspension of iinely divided silicaand a caustic alkali; spray drying the resulting reaction mixture andthereafter fracturing, pulverizing and agitating the spray dried productto form particles having continuously even surfaces.

In accordance with a method embodiment of the present invention, anaqueous suspension or dispersion of finely divided silica (SiOz) and analkali hydroxide, e.g., sodium hydroxide, are subjected to hydrothermaltreatment for a period of time suicient to transform the reactants intoalkali metal silicates that are at least partially polymerized andwhich, as stated above, contain polysilicate ions in a polymerized,irreversible state.

As used herein the term finely-divided silica refers to a nely dividedpowder containing at least 99% SiO2 and having a particle size at least95% of which are no larger than 75 microns. Silica powders, referred toin the art as silica Hour or its equivalent are suitable.

The alkali metal hydroxide employed in the present invention ispreferably sodium hydroxide (NaOH). However, other alkali metalhydroxides, i.e., metals of Group Ia of the Periodic Table may beemployed. These include potassium, lithium, rubidium, cesium andfrancium hydroxide.

At this point it may be noted, and as is generally known in the art,alkali metal silicates having a silica to sodium oxide weight ratio(SiO2/Na20) on the order of about 1.5:1 are in simple ionic form. Asindicated, the present invention is directed to a process for making analkali metal polysilicate that is at least partially polymerized.Therefore the concentration of the reactants i.e., silica and the alkalimetal hydroxide, is critical to the extent that said concentrations mustbe such that the SiO2/Na20 weight ratio of the product is at least1.8:1. In accordance With the present invention, it has been discoveredthat products having SiO2/Na20 weight ratios of from about 1.8:1 to 2.7:1 are particularly advantageous. Thus in a preferred practice of theinvention and when employing NaOH (expressed as NaZO) as the alkalimetal hydroxide, the initial composition of the reactants (on a drybasis) is from about 64 to 74 percent by weight SiO2 and from about 36to 26 percent by weight NazO. The amount of water employed is criticalto the extent that the reaction mixture must be fluid. Also it has beenfound that very dilute reaction mixtures effect a substantial decreasein the rate of reaction. Preferably, the weight percent of the water,based on the total weight of the reaction mixture, is from about to 60percent.

As will be described in more detail hereinafter, the hydrothermaltreatment of the aqueous dispersion of tinely divided silica andhydroxide is effected in a closed vessel at temperatures above theboiling point of the aqueous suspension being treated and under theelevated pressures obtained at such temperatures. Any suitablepressurized equipment, provided with means for maintaining the aqueousmixture under high agitation and provided with means (e.g., a steamjacket) for maintaining the dispersion at the desired temperatures andpressures, may be employed.

In this regard, the hydrothermal treatment of the silica/ der constantagitation during the charging as well as the reaction period. Ifdesired, the concentrated caustic solution may be preheated to thereaction temperature prior to the introduction of the silica slurry. Ifthe caustic solution is not preheated, the aqueous solution containingthe silica and hydroxide is initially preheated to that temperature atwhich the hydrothermal synthesis is to be conducted. The reactionmixture is maintained at the preselected reaction temperature, againwhile maintaining same under continuous agitation, for a period of timet0 effect substantially complete transformation of the silica andhydroxide into the alkali metal polysilicate.

At the end of the reaction period, the reaction vessel is vented and themixture is passed, preferably by gravity, into a drop tank 2 whichcontains dilution water at approximately room or ambient temperatures.In this manner the temperature and the reaction mixture is cooledquickly and efhciently and the weight ratio of the reaction product towater adjusted to the concentration required for the spray drying of theproduct as described hereinbelow.

The aqueous mixture in the drop tank is preferably passed through aclarification filter 3 to remove small quantities of insolubles, such assand, unreacted silica and the like. As illustrated in the embodimentshown in IFIG. 2, the clarified aqueous mixture may then be passed intoa hold or storage tank 4, or fed directly into the upper portion of aspray dryer, indicated generally at 5.

With reference to FIG. 1, the aqueous mixture is introduced into theupper portion of the generally upright or vertical, cylnidrical chamber6 of the spray dryer 5 and passes through a rotating wheel or spraynozzle 7. The latter causes the aqueous mixture to be finely and evenlydispersed Within said chamber and in direct contact with a mass ofupwardly directed hot gas, i.e., air, introduced through conduit means8. Suitable control valves (not shown) may be provided for regulatingthe rate of feed of the reaction mixture, as Well as that of upwardlydirected air, into the spray dryer. In accordance with the presentinvention, the spray drying is preferably elfected at relatively hightemperatures, with particularly advantageous inlet air temperaturesbeing on the order of from about 400 F. to 1000 F. :In this manner, theflashing off of the water in the spray dryer is effected rapidly withthe resultant spray dried droplets being in the form of hollowmicrospheres.

.Turning now to the details of the post-processing techniques employedin the practice of the present invention, the spherical polysilicateparticles are collected at the bottom of the spray dryer and fed (as bya screw conveyor) into a suitable milling apparatus 9 which serves tofracture and pulverize the hollow spheres so that the denslty of theresulting fractured particles is increased to i at least 25 lbs/cubicfoot.

caustic dispersion may be conducted at temperatures in v the range offrom about 280 F. to 410 F. and corresponding pressures of aboutp.s.i.g. to 290 p.s.i.g., respectively. Preferred temperature ranges arefrom 310 F. to 350 F. The reaction time is a function of the temperatureemployed. Reaction periods on the order of about 2.5-4.5 hours arerequired for the above identified temperature ranges, it being of courseunderstood f The fractured and pulverized particles are next passed intoa rotating drum or cylinder 10 which serves to reduce the surfaceirregularities of the fractured particles and to form a product havingcontinuously even surfaces. In this regard the temperature of thefractured particles in the rotary drum is preferably in the range offrom to 140 C. At a temperature on the order of about 70 C. or higher,the particles become somewhat plastic 1n nature. It has been found thatthis characteristic is preferable in obtaining the desired reduction ofthe surface lrregularities of the particles, i.e., obtaining a producthaving continuously even surfaces.

The rotary drum or apparatus is thus preferably a rotary dryer whichserves the dual function of effectively reducing the surfaceirregularities as well as reducing the moisture content of the productto a desired level. A single rotary dryer is sufficient to reduce themoisture content of the product to approximately 18%. However,additional secondary rotary dryers, indicated at 10', may be employed ifrequired. The dried product may be passed through suitable screeningapparatus to produce a product having a desired particle size or range.In accordance with U.S. Ser. No. 193,471 led Oct. 28, 1971, and againwith reference to FIG. 1, the fractured and pulverized product from themilling apparatus may alternately be fed into a pelletizer indicatedgenerally at 11, and then into a secondary dryer 12. While the apparatusemployed in the post-processing techniques of the invention e.g., mills,rotary dryers, etc. are Well known per se, the sequence steps disclosedherein are unique to the extent that polysilicate products havingparticularly desirable properties, i.e., a percent moisture content ofless than 20 percent, a density on the order of 40-46 lbs/cubic foot anda particle size of minus 14 plus 65 mesh (Tyler screen size), can beproduced from a high temperature spray dried product.

As will be readily appreciated by those skilled in the art, the uniqueprocess of the present invention may be carried out batchwise or on asemi-continuous or continuous basis. As known, continuous orsemi-continuous processes involve a continuous mixing operation in whichthe reactants, i.e., the silica and sodium hydroxide, are continuouslyproportioned into a suitable reaction vessel, the reaction mixture thenbeing continuously discharged therefrom. Since the reaction time of thepresent invention is on the order of 2.5-4.5 hours a continuousoperation would generally require a number of reactors or autoclaves inseries so that the required retention time could be established.Alternately an elongated tubular reactor, provided with suitablebaffles, heat transfer means, etc., could be designed.

Before turning to specific examples of the present invention, and againas briefly discussed above, the unique alkali metal polysilicates of thepresent invention have particular utility for use as builders indetergent compositions. Thus an important object of the invention is toprovide a detergent composition comprising a surfactant and, as abuilder, the novel polysilicates of the present invention, the latterbeing employed as a direct replacement for polyphosphates. In thisregard, the builder of the invention may be used with any of theconventional detergent classes, i.e., synthetic non-soap anionic,nonionic and/or amphoteric surface active compounds which are suitableas cleansing agents. Anionic surface active compounds can be broadlydescribed as compounds which contain hydrophilic or lyophilic groups intheir molecular structure and which ionize in an aqueous medium to giveanions containing the lyophilic group. These compounds include thesulfated or sulfonated alkyl, aryl and alkyl aryl hydrocarbons andalkali metal salts thereof, for example, sodium salts of long chainalkyl sulfates, sodium salts of alkyl naphthalene sulfonic acids, sodiumsalts of sulfonated abietenes, sodium salts of alkyl benzene sulfonicacids particularly those in which the alkyl group contains from 8-24carbon atoms; sodium salts of sulfonated mineral oils and sodium saltsof sulfosuccinic acid esters such as sodium dioctyl sulfosuccinate.

Advantageous anionic surfactants include the higher alkyl aryl sulfonicacids and their alkali metal and alkaline earth metal salts such as forexample sodium dodecyl benzene sulfonate, sodium tridecyl sulfonate,magnesium dodecyl benzene sulfonate, potassium tetradecyl benzenesulfonate, ammonium dodecyl toluene sulfonate, lithium pentadecylbenzene sulfonate, sodium dioctyl benzene sulfonate, disodium dodecylbenzene disulfonate, disodium diisopropyl naphthalene disulfonate andthe like as well as the alkali metal salts of fatty alcohol esters ofsulfuric and sulfonic acids, the alkali metal salts of alkyl aryl(sulfothioic acid) ethers and the alkyl thiosulfuric acid, etc.

Nonionic surface active compounds can be broadly described as compoundswhich do not ionize but usually acquire hydrophilic characteristics froman oxygenated side chain, such as polyoxyethylene, while the lyophilicpart of the molecule may come from fatty acids, phenols, alcohols,amides or amines. Examples of nonionic surfactants include productsformed by condensing one or more alkylene oxides of 2 to 4 carbon atoms,such as ethylene oxide or propylene oxide, preferably ethylene 6 oxidealone or with other alkylene oxides, with a relatively hydrophobiccompound such as a fatty alcohol, fatty acid, sterol, a fatty glyceride,a fatty amine, an aryl amine, a fatty mercaptan, tall oil, etc. Nonionicsurface active agents also include those products produced by condensingone or more relatively lower alkyl alcohol amines (such asmethanolamine, ethanolamine, propanolamine, etc.) with a fatty acid suchas lauric acid, cetyl acid, tall oil fatty acid, abietic acid, etc. toproduce the corresponding amide.

Particularly advantageous nonionic surface active agents arecondensation products of a hydrophobic compound having at least 1 activehydrogen atom and a lower alkylene oxide (for example the condensationproduct of an aliphatic alcohol containing from about 8 to about 18carbon atoms) and from about 3 to about 30 mols of ethylene oxide permol of the alcohol, or the condensation product of an alkyl phenolcontaining from about 8 to about 18 carbon atoms in the alkyl group andfrom about 3 to about 30 mols of ethylene oxide per mol of alkyl phenol.Other advantageous nonionic detergents include condensation products ofethylene oxides with a hydrophobic compound formed by condensingpropylene oxide with propylene glycol.

Amphoteric surface active compounds can be broadly described ascompounds which have both anionic and cationic groups in the samemolecule. Such compounds may be grouped into classes corresponding tothe nature of the anionic-forming group, which is usually carboxy, sulfoand sulfato. Examples of such compounds include sodium N-coco beta aminopropionate, sodium N-tallow beta amino dipropionate, sodium N-laurylbeta iminodipropionate and the like.

Other typical examples of these categories of the anionic, nonionicand/or amphoteric surface active agents are described in Schwartz andPerry Surface Active Agents Interscience Publishers, New York (1949) andthe Journal of American Oil Chemists Society, volume 34, No. 4, pages-216 (April 1975) which are incorporated herein by reference.

The amount of polysilicate builder necessary to be used with the surfaceactive compound (active) may vary upon the end use, type of activeemployed, pH conditions and the like. In general, the builders can beemployed in detergent compositions in any desired proportions. Theoptimum active/builder ratio depends upon the particular active employedand the end use for which the detergent composition is intended but mostgenerally will fall within the range of active/ builder weight ratio ofabout 10:1 to 1:10 and preferably about 4:1 to 1:4.

Detergent compositions produced in accordance with the present inventioncan be prepared in any of the commercially desirable composition formssuch as bar, granular, ake, liquid and tablet form. It should beunderstood that the present invention is not limited to any particularmethod for preparing the detergent compositions containing the builderand the surfactant. Such techniques are well known in the industry.Thus, e.g., the builder may be mechanically mixed in the surfactant inthe form of a slurry or dissolved in a solution of the surfactant.Additionally, the builder may be admixed with the surfactant in any ofthe forms in which the surfactant is manufactured.

The invention will be further illustrated by the following exampleswhich set forth particularly advantageous method and compositionembodiments. While the examples prove to illustrate the presentinvention they are not intended to limit it thereto.

PREPARATION OF ALKALI-METAL POLYSILICATES Example 1 9,476 lbs. of a 50%NaOH solution was charged to a stainless steel autoclave provided withmeans for continuously agitating the solution. A silica slurry, preparedby dispersing 9,269 lbs. of silica flour into 5,054 lbs. of water, wasthen charged to the reactor. The autoclave was sealed and thetemperature of the aqueous mixture preheated (by the introduction ofsteam into an exterior steam jacket) to 315 F. (100 p.s.i.g.) over aone-hour period. The reaction mixture was thereafter maintained at thistemperature for three hours. Continuous agitation was maintainedthroughout the heat up and reaction period. At the end of the three hourreaction cycle, the steam was shut oif and the autoclave partiallyvented to reduce the pressure to about 60 p.s.i.g. The vent was thenfully opened, the pressure in the autoclave being reduced to 20 p.s.i.g.At this time a bottom outlet valve of the autoclave was opened and thereaction mixture fed by gravity into a drop tank positioned beneath theautoclave and containing 15,144 lbs. of H2O at 77 F. The mixture in thedrop tank was pumped through a classification filter and introduced intothe upper portion of a spray dryer of the type illustrated in FIG. 1.The aqueous mixture was fed into the spray dryer at a rate of 21,100lbs. per hour, the concentration of the mixture comprising 4 lbs. ofsodium polysilicate per gallon. The speed of the spray Wheel or nozzlewas about 11,000 r.p.m. The spray dryer inlet and outlet airtemperatures were 600 F. and 200 F. respectively. The spray driedproduct was collected and withdrawn from the base of the spray dryer bya screw conveyor and passed into a high impact mill which fractured andpulverized the spherical particles. In this example 12,480 lbs. ofsodium polysilicate, having a SiO2Na2O weight ratio of 2.4:1 and adensity of 24#/ft.3 was recovered from the spray dryer. The millingoperation increased the density of the product to about 38#/ft.3. Theproduct was next passed into a rotary dryer which reduced the moisturecontent of the polysilicate particles from about 25% to about 18%. Inaddition it was found that the tumbling action of the rotary dryer hadthe effect of rounding off the sharp edges of the fractured particlesfrom the milling action so that the particles had continuously evensurfaces. The fact that the product produced in this example waspartially polymerized was established by conductivity tests asdetermined by the Harman technique (R. W. Harman, Journal f PhysicalChemistry 32, 44-60 (1928).

Example 2 The procedure of Example 1 was repeated except that thetemperatures and pressures of the hydrothermal reaction were varied in aseries of examples as shown by the following table.

TABLE 1 Tempela- Reaction ture Pressure time Run No. F.) (psig.)(minutes) Example 3 In this example the general procedures of Examplesl-2 were repeated except that, in a series of tests conducted on a benchor laboratory scale basis, potassium, lithium, and cesium hydroxide weresubstituted for the sodium hydroxide. In these tests, to save time andexpense, small quantities of the reactants, eg., 132.6 grams potassiumhydIQxide, 92.69 grams silica flour and 50.54

grams of H2O were employed in laboratory equipment. However, these testsproduced products having properties substantially the same as theproduct of Example 1;

Example 4 In a series of tests the procedures of Example 1 Were repeatedexcept that the quantities of reactants in the hydrothermal treatmentwere varied as indicated.

In order to illustrate the use of the unique polysilicates, produced inaccordance with the present invention, as builders in detergents, apolysilicate builder was compared under carefully controlled conditions,with sodium tripolyphosphate, sodium carbonate and a conventional sodiumsilicate. To obtain as accurate a measurement as possible of the builderproperties of each of the compounds, none of the usual additives, suchas fabric softener-s, were used in the following tests. The tests weremade in a Terg-O-Tometer machine on standard soiled fabric specimens.The surfactant employed was sodium dodecylbenzene sulfonate with a 122.6ratio of surfactant to builder. The test results are as shown in Table 3below.

TABLE 3 Builder in formulation, Builder only, percent percent Reilec-Soil Reflec- Builder Ash tance removal Ash tance Unsoiled cloth 0. 03100. 0 0. 04 100 STPP:

0. 03 97. 3 35 0. 13 99. 7 (2) 0. 05 97. 1 35 0. 05 99. 4 NaaCOa (l) 1.19 94. 3 26 0. 71 94. 6 (2) 1. 19 94. 4 25 0. 66 95. 5 Known sodiumsilicates:

0. 37 98. 7 30 0. 37 98. 7 o 0. 37 9S. 6 30 0. 87 98. 6 Polysilieates ofInvention, Products of- Example 1 0.05 98. 5 35 0. 13 99. 0 Example 2".0. 03 98. 6 35 0. 13 99. 5 Example 5:

Run (1) 0. 18 98. 5 35 0. 13 99. 0 Run (3) 0. 08 98. 5 35 0. 13 98. 9Run (5) 0. 06 98. 6 35 0. 13 99. 1 Run (7 O. 05 98. 6 35 0. 13 99. 3

The above results indicate that the polysilicate builder of the presentinvention compares very favorably with sodium tripolyphosphate and issuperior to conventional sodium silicates and sodium carbonates.Further, and as will be readily appreciated by those skilled in the art,the low ratio (SiOg/NazO) silicates currently commercially available arerelatively expensive and are often not available in dry form because ofhigh production cost and solubility factors common to e.g., glassfurnace (fusion) silicate processes.

Thus it will be seen that the present invention provides a truly uniqueand simplified process for producing alkali metal polysilicates thathave particular use as builders in detergents. The process of theinvention permits high iiexibility in the production of a product of anygiven or desired properties.

As used herein detergent(s) refers to washing compositions in generalincluding laundry detergents, dishwashing compounds and relatedmaterials. The term agitating as used herein refers to subjecting theparticles to motion, most commonly tumbling motion to reduce surfaceirregularities and/or agglomerate. The range of polysilicate compositionobtainable is controlled by reactor charge and includes SiO2/Na20 weightratiosof `1:1 to

9 26:1, preferably in the range 2:1 to 2.4:l. An importantcharacteristic of these products is the controlled hydration whichaffects solubility and hence the functional utility of these products indetergency applications.

Density, particle sizes, particle shape and size distribution, andmaterials handling properties are irnportant characteristics of theproducts of the present invention which may control these propertiesover a broad range. For example density may be varied from 0.4 g./cc.(25 lbs./ft.3) to in excess of 0.96 g./cc. (60 lbs./ft.3) whilemaintaining a size distribution of maximum on a 65 mesh screen. It isalso possible to produce the above mentioned density range but vary thesize distribution so that substantially 100% of the particles areretained on a 65 mesh screen. The product of the present invention maybe incorporated into detergent compositions as a pre-drying orpost-drying additive.

Although a specic preferred embodiment of the present invention has beendescribed in the detailed description above, the description is notintended to limit the invention to the particular forms or embodimentsdisclosed herein, since they are to be recognized as illustrative ratherthan restrictive and it will be obvious to those skilled in the art thatthe invention is not so limited. The invention is declared to cover allchanges and modications of the specific example of the invention hereindisclosed for purposes of illustration, which do not constitutedepartures from the spirit and scope of the invention.

What is claimed is:

1. A method for producing alkali metal silicate particles havingparticular utility for use in detergents, said method comprising thesteps of subjecting an aqueous dispersion including linely dividedsilica and an alkali metal hydroxide, selected from the group consistingof sodium, potassium, lithium, and cesium hydroxide, to hydrothermaltreatment at a temperature in the range of from about 280 F. to 410 F.for a period of time effective to react said silica and said hydroxideto form a silicate that is partially polymerized; said dispersion ofsaid silica and hydroxide having an SiOz/NazO Weight ratio of at least1.8:1; passing said reaction mixture into the upper portion of a dryingchamber and dispersing said mixture in the form of line droplets in saidchamber; contacting said droplets with a mass of upwardly directed airat a temperature of at least 400 F. suicient to dry said droplets in theform of minute hollow spheres; fracturing and pulverizing said hollowspheres so that the density of the resulting fractured particles is atleast 30 pounds per cubic foot; agitating the fractured particles Whilemaintaining said particles at a temperature of at least C. to round offthe sharp edges thereof and contacting said particles With a mass of airat a temperature sufficient to reduce the moisture content of saidparticles to less than 25 percent.

References Cited UNITED STATES PATENTS 3,687,640 8/1972 Sams et al23-313 1,111,918 9/1914 Paterson 423-334 2,881,049 4/1959 Erbe et al.423-332 1,198,203 9/1916 Edgerton 423-334 1,517,891 12/1924 Dickerson423-3 32 1,119,720 12/1914 Paterson 423-334 FOREIGN PATENTS 203,749 9/1923 Great Britain 423-333 EDWARD J. MEROS, Primary Examiner U.S. C1.XR.

